1. Field of the Invention
This invention relates to closure fastening devices, and more particularly, to interlocking closure fastening devices having controlled separation characteristics.
2. Description of the prior Art
Generally, closure fastening devices for use with plastic bags and the like are well-known. In addition, manufacturing methods for closure devices made of plastic material are generally known.
Closure fastening devices for use with plastic bags should be relatively easy to open and close and also provide a satisfactory seal. However, prior art closure fastening devices sometimes lack significant controlled separation characteristics. The controlled separation of a closure device may be described as its ability not to open freely much more than the initial gap induced by the separating force of the user. This lack of significant controlled separation manifests itself during opening of a plastic container or bag and is especially troublesome to a user during the closing or sealing operation of the container. More specifically when plastic bags having closure fastening devices are partially opened, they can continue to open completely with little or no separating force applied to the fastening devices. Such a characteristic is desirable for opening the plastic bag but presents a disadvantage on closure since the user often desires to expel the preponderance of air from the bag prior to sealing. This is most desirably accomplished if the major portion of the fastening device is interlocked, and only a small aperture remains for expelling most of the residual air from the bag before accomplishing the final closure and sealing.
Various types of such closure fastening devices may be connected to the opening of a container to form a container capable of being closed and opened. One such closure fastening device employed with a container is available from Dow Chemical Company. Midland, Mich. under the tradename ZIPLOC.RTM.. This closure fastening device comprises a first groove or female element having hook portions facing towards each other, and a second rib or male element which is arrowhead-shaped. The upper, or outside (relative to the interior of the container), engaging surface of the rib element is shorter than the lower, or inside, engaging surface of the rib element. When employed with a container, the container opens relatively easily from the outside and resists opening from the inside. Although providing some controlled opening characteristics, such a closure fastening device has a tendency to twist and distort during attempted occlusion, and thus is somewhat difficult to occlude.
Another closure fastening device employed with a container is provided by Union Carbide Corporation. Danbury, Conn., and is commercially available under the tradename SNAP LOCK.RTM.. This closure fastening device is provided with U-shaped channel elements comprising a first channel element including hook portions facing away from each other, and a second straddling channel element including hook portions facing towards each other. The channel elements interlock by pressing the first channel element into the second channel element so that the hook portions engage each other. When employed with a container, this device possesses differential deocclusion characteristics, i.e., it is easier to open from the outside of the container than from the inside of the container. Although generally easier to occlude than the Dow Chemical Company device, this fastening device does not provide significant controlled opening characteristics during deocclusion.
Another closure fastening device employed with a container is manufactured by presto products. Inc., Appleton, Wisconsin, and is available through Certified Grocers, Inc., Hodgkins, Ill. under the tradename Household Delight.RTM.. This closure fastening device comprises first and second closure elements, and further has a linear projection positioned laterally away from each of the hook portions of the first closure element, and a linear projection positioned between the hook portions of the second closure element which extends into the cavity of the hooks of the first closure element. Although providing controlled opening characteristics as a result of its substantial mass, this closure fastening device comprises a configuration having many sections requiring relatively large amounts of resin material resulting in greater material costs and likely involving a more complicated production process.
Thus, it would be desirable to provide a closure fastening device connected to a container wherein the closure fastening device has good handling properties and controlled opening characteristics while retaining a simplified structure requiring a minimum amount of resin material. This in turn would reduce cooling requirements during production, enable the use of small extruders, and require less energy per production unit.
Thus there is a continuing need to provide closure fastening devices which overcome the above-noted disadvantages and have a controlled resistance to deocclusion.